Updates to Team Fortress 2 have been released. The updates will be applied automatically when your Steam client is restarted. The specific changes include:

Added Multicore Rendering

* This initial release is aimed at testing compatibility, so the option is OFF by default
* To turn it on, go to the Options->Video->Advanced dialog, and check the "Multicore Rendering" option

Other Changes

* Several performance improvements to decals and client bone/flex setup
* A variety of alt-tab and mode switch fixes
* Improvements to the way the engine initializes surround sound, fixing some specific hardware cases
* Fixed a crash on exit in Vista 64